This had mixed results, but trying sharp angles angles (sharper than above) and long exposure times generally worked. We played a little with different sides of the chip. In all tests main EPROM was untouched.

Not perfect, but should be good enough for the real chip. Masking:

And tried a few angles until the security fuse got cleared. Yipee!

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Monday, May 1, 2017

A bit back we processed PIC16C57 samples and discovered#139 (Invasion U76) was partially defective as received. We knew this before decap since PIC16C57 allows reading a 4 bit XOR of the 12 bit flash worlds even when protected. Unfortunately, only 2/4 word bits changed in the protected readout and only 3/12 word bits changed in the unprotected version.

Like Invasion, Mortal Kombat 4 is built on the Midway Zeus platform. With this in mind, a team member donated U76 from Mortal Kombat 4 to process as a replacement. Label off:

Thursday, February 23, 2017

In this post we look at obtaining the Fujitsu MB86233 ROM for the following:

#14 Sega 315-5571

#15 Sega 315-5572

#16 Sega 315-5573

First decap a sample chip to get more information. Here's 315-5571:

Which tells us it's contact programmed:

Under 20x brightfield illumination:

Our computer vision expert was concerned automatic capture would be noisy and asked for a 100x die scan. Unfortunately, 100x takes a long time. Fortunately, a quick test showed a 20x scan with crossed polarizers has sufficient SNR:

We then fed this into computer vision tools like on 39. Finally, ROM bit order was swapped around until it disassembled relatively cleanly. Unfortunately, instruction set documentation is incomplete meaning even correct bit ordering may produce disassembler errors.

Chips around #211 - 218 are suspected to be similar chips and we might take a look at them in the near future.

Saturday, January 28, 2017

Side note: post was supposed to go out early release to backers but accidentally went to general release. We apologize to the backers, but it got a lot of attention in the short time that it was out, so we think it is best at this point to just keep it out there. We'll fix this for future posts.

First part is same idea as #45 but on a smaller scale: assess and repair damage. Sample as received:

Close up:

The chip has been opened and 5 pins are missing at the bottom. Bond wires are in general disarray and the die is dirty:

However, no obvious silicon damage. After ultrasonic clean:

This allowed a closer inspection under a higher power microscope that also revealed no damage.

Among the 5 broken wires are 3 address bits, reset, and one from P3. P3 is unused during readback, so we really only need to fix 4 of them.

Start by rebuilding leadframe. First, epoxy everything still intact:

This helps prevents damage when inserting into a socket. Next, inserted into a socket to improve mechanical stability and provide a template for the new pins:

Then a sacrificial 8751 was stripped of its pins (see 45 post for process details) and epoxied into the leadframe:

During wire attach, previous work put epoxy on the die surface to use as a fine palate. Although this is likely harmless, can possibly scratch the die and/or short something out. Decided to put the security fuse UV mask on early to double as a mask and a protective barrier:

Wires are also soldered up now:

And add epoxy:

After cure tried dumping and still getting address failures with several bits stuck at 0. Although pin resistance values are not in spec to other similar pins, they are close. Suspect that epoxy got too close to die edge and is doing some sort of soft short.

However, this whole time data bits have also been flaky. At least one wire was broken and was repaired with silver conductive epoxy. However, we are unable to determine why data lines are flaky.

Fortunately, dumps were taken at many steps of this process. In fact, at least three dumps had all address bits correct but varying data bits bad. Several of these dumped the same twice meaning the data is incomplete but reasonably stable.

Wrote a small bit of code to combine the good bits from each dump. This also showed that dumps agree on bits common between them.

Next, popped combined dump into a disassembler to verify reasonable control flow. Cursory check revealed no errors. Finally, dump was simulated and showed no obvious issues.

In conclusion, 204 was salvageable but was a bit of a puzzle to piece together. Several verification methods indicate its probably good. Hopefully this is the last of the samples requiring such repairs.

Wednesday, January 25, 2017

In this edition we look at obtaining the PIC16C57 ROM for the following:

234: World Beach Volleyball

241: Ultimate Mortal Kombat

242: World Rampage

The following showed data loss at receipt and, as a result, were not processed successfully:

139: Invasion (some bits)

227: Action Hollywood (some bytes)

241/242 are found as U64 on Midway Wolf Unit game boards. Board repair logs indicate this part commonly failed. Extracted MCU ROMs can now be used to create replacement parts.

These chips are a bit unusual in several ways. First, they use 12 bit words. Second, code protection intentionally leaks a 4 bit xor of the 12 bit words. Therefore, even with protection enabled you can glean quite a bit about the firmware. We went with a UV attack, but this might also make them vulnerable to programming one nibble at a time and observing the xor difference. Anyway, all chips are dumped as received ("protected dump").

Same idea as the 8751: mask the main EPROM while keeping the security fuse exposed to UV light. All chips were still packaged when received. The first three were easy:

But 227 was received in poor condition:

Pins straightened, but pin 1 still missing. Some debate about whether it was necessary, but couldn't get a good dump without it

Tried soldering but couldn't get anything to stick:

So ground down the package to get more grab:

Which allowed soldering on a pin (solid wire):

but this kept snapping off in the ZIF socket due to slight misalignment. So instead fitted something more flexible:

and got a dump (after de-protecting).

Unfortunately, the protected dump indicates that the first 0x40 words were 0'd. We hoped that de-protecting was going to shed more light on this but did not. Its unknown if this was accidentally erased at some point, the silicon is damaged, or what. Finally, we do not believe we accidentally programmed this. Aside that we don't recall issuing a program command, our programmer defaults to 0xFFF, not 0x000.

139's protected dump has only 2 / 4 bits and the unprotected dump has only 3 / 12 bits. No die damage is visible. We do not yet have a theory as to what happened to this chip.

To summarize, 234, 241, and 242 were dumped successfully. We believe 139 was corrupted before we got it. Similarly, 227 was received bad and its unclear if we can fix it. If the community has replacements for 139 or 227 we'd like to acquire them rather than spending more time investigating.